1. Field of the Invention
The present invention relates to a method of managing a queuing operation for a wireless communications system and related communications device, and more particularly to a method of managing a queuing operation corresponding to a cell update procedure in a wireless communications system and related communications device.
2. Description of the Prior Art
The third generation (3G) mobile communications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA can provide high frequency spectrum utilization, universal coverage, and high quality, high speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse flexible two-way transmission services and better communication quality to reduce transmission interruption rates.
For the universal mobile telecommunications system (UMTS), the 3 G communications system comprises User Equipment (UE), the UMTS Terrestrial Radio Access Network (UTRAN), and the Core Network (CN). Communications protocols utilized include Access Stratum (AS) and Non-Access Stratum (NAS). AS comprises various sub-layers for different functions, including Radio Resource Control (RRC), Radio Link Control (RLC), Media Access Control (MAC), Packet Data Convergence Protocol (PDCP), and Broadcast/Multicast Control (BMC). The sub-layers mentioned, and their operating principles, are well known in the art, and detailed description thereof is omitted.
RRC is a Layer 3 communications protocol, and is the core of the AS communications protocol. All radio resource information exchange, radio resource configuration control, QoS control, channel transmission format configuration control, packet segmentation/concatenation processing and control, and NAS protocol transmission processing is performed by the RRC layer. Between the user end and the network end, the RRC layer exchanges RRC Messages, also known as signaling, through RRC procedures. RRC Messages are formed from many Information Elements (IE) used for embedding necessary information for setting, changing, or releasing protocol entities of Layer 2 (RLC, MAC) and Layer 1 (Physical Layer), thereby establishing, adjusting, or canceling information exchange channels to perform data packet transportation.
According to the RRC protocol specification developed by the 3rd Generation Partnership Project (3GPP), the RRC procedures include a cell update procedure, which is initiated by the UE in response to certain events in UE e.g. uplink data transmission, paging response, or cell reselection. The RRC message exchange in the cell update procedure includes a CELL UPDATE message transmitted from the UE to the UTRAN, and a CELL UPDATE CONFIRM message transmitted from the UTRAN to the UE. According to content of the CELL UPDATE CONFIRM message, the UE performs radio bearer reconfiguration or release, mobile information update, or transport channel reconfiguration, etc.
During the cell update procedure, the UTRAN can utilize a queuing operation to queue the UE when the current serving frequency carrier is congested. Under the queuing operation, the UE is directed to another frequency carrier for a certain time and re-initiates the cell update procedure. The related detailed operation is described as follows. After the UE transmits the CELL UPDATE message after the initiation of the cell update procedure, the UTRAN includes a “Frequency info” IE and a “wait time” IE in the CELL UPDATE CONFIRM message in response to the CELL UPDATE message for indicating the UE to perform the queuing operation. After receiving the CELL UPDATE CONFIRM message, the UE in CELL_PCH state selects a dedicated cell on the new frequency carrier, whereas the UE in the URA_PCH state selects a cell belonging to the dedicated URA. After the cell selection, the UE waits at least the time given by the “wait time” IE, and then reinitiates the cell update procedure. The frequency carrier indicated in the wait time IE is never the current frequency carrier the UE uses.
The nearby frequency carriers could be more congested when the serving frequency carrier of the UTRAN is congested, or no other frequency carrier is available. In these situations, it is not proper or impossible for the UTRAN to queue the UE on other frequency carriers.